The changes in physical and chemical properties of a few enzymes as a function of age are investigated. The enzymes are cytoplasmic superoxide dismutase (SOD) of rat liver, heart and brain, nematode fructose-1,6-diphosphate aldolase and mouse liver ornithine decarboxylase (ODC). It has been found that as a function of age the only properties of these enzymes which are noticeably changed are heat sensitivity and specific activity per mg purified protein or per unit enzyme antigen. Km, molecular weight, electrophoretic mobility, Ki for inhibitors and antigenic identity do not change in all three enzymes as a function of age. Also, no specific changes in amino acid composition of these enzymes from animals of various age groups has been found. However, preliminary results indicate specific changes in peptide patterns after tryptic digestion when SOD from young and old animals is compared. The chemical cause of these changes is not yet determined. Nematode aldolase and ODC show increasing half-life values as a function of age. These increases are 8-fold and 2-fold for aldolase and ODC respectively. Also, the turnover of total proteins in nematodes as they age, decreases considerably. The causes of this decrease in turnover are being investigated. BIBLIOGRAPHIC REFERENCES: Gershon, D. and Gershon, H. (1976) The Evaluation of the "Error Catastrophe" Theory of Ageing in Light of Recent Gerontology (in press). Reiss, U. and Gershon, D. (1976) Rat Liver Superoxide Dismutase: Purification and Age-related Modifications. Europ. J. Biochem. (in press).